Re: [PATCH for-next 1/2] RDMA/hns: Add the workqueue framework for flush cqe handler

[Jason Gunthorpe <jgg@ziepe.ca>]

On Thu, Nov 07, 2019 at 08:48:25PM +0800, Liuyixian (Eason) wrote:
> 
> 
> On 2019/11/7 4:40, Jason Gunthorpe wrote:
> > On Mon, Oct 28, 2019 at 05:45:44PM +0800, Yixian Liu wrote:
> >> @@ -1998,6 +2000,17 @@ static int hns_roce_v2_init(struct hns_roce_dev *hr_dev)
> >>  		}
> >>  	}
> >>  
> >> +	snprintf(workq_name, HNS_ROCE_WORKQ_NAME_LEN - 1,
> >> +		 "hns_roce_%d_flush_wq", device_id);
> >> +	device_id++;
> >> +
> >> +	hr_dev->flush_workq = alloc_workqueue(workq_name, WQ_HIGHPRI, 0);
> >> +	if (!hr_dev->flush_workq) {
> > 
> > Why is this so time critical?
> 
> Hi Jason,
> 
> I am not quite sure whether you concerned with the flag "WQ_HIGHPRI" or
> why WQ is created in hns_roce_v2_init.

Yes, why do you need a dedicated HIGHPRI work queue.

> If it is WQ_HIGHPRI, yes, it is much better to implement flush operation
> ASAP to help generating flushed cqe as ULP may poll cqe urgently. If you
> concerned allocation stage, as flush operation is support for hip08 only,
> there is no other place proper than here I think.

Why? This is only something that happens in error cases.

> > Why don't you do this from hns_roce_irq_work_handle() ?
> 
> As described in the cover letter, here we used CMWQ (concurrency management workqueue)
> to make sure that flush operation can be implemented ASAP. Current irq workqueue is
> a singlethread workqueue, which may delay the flush too long when the system is heavy.
> 
> Do you mean we can change irq workqueue to CMWQ to put flush work into it?

As far as I could tell the only thing the triggered the work to run
was some variable which was only set in another work queue 'hns_roce_irq_work_handle()'
 
> >> +}
> >> +
> >> +void init_flush_work(struct hns_roce_dev *hr_dev, struct hns_roce_qp *hr_qp)
> >> +{
> >> +	struct hns_roce_flush_work *flush_work;
> >> +
> >> +	flush_work = kzalloc(sizeof(struct hns_roce_flush_work), GFP_ATOMIC);
> >> +	if (!flush_work)
> >> +		return;
> > 
> > Don't do things that can fail here
> 
> Do you mean that as "GFP_ATOMIC" is used, the if branch can be deleted?

No, don't do allocations at all if you can't allow them to fail.

Jason